// This file is published under public domain.
// Originially from https://github.com/kokke/tiny-AES-c.

// This is an implementation of the AES algorithm, specifically ECB, CTR and
// CBC mode. Block size can be chosen in aes.h - available choices are AES128,
// AES192, AES256.
//
// The implementation is verified against the test vectors in:
//   National Institute of Standards and Technology Special Publication
//   800-38A 2001 ED
//
// ECB-AES128
// ----------
//   plain-text:
//     6bc1bee22e409f96e93d7e117393172a
//     ae2d8a571e03ac9c9eb76fac45af8e51
//     30c81c46a35ce411e5fbc1191a0a52ef
//     f69f2445df4f9b17ad2b417be66c3710
//   key:
//     2b7e151628aed2a6abf7158809cf4f3c
//   resulting cipher
//     3ad77bb40d7a3660a89ecaf32466ef97
//     f5d3d58503b9699de785895a96fdbaaf
//     43b1cd7f598ece23881b00e3ed030688
//     7b0c785e27e8ad3f8223207104725dd4
//
// String length must be evenly divisible by 16byte (str_len % 16 == 0).
// You should pad the end of the string with zeros if this is not the case.
// For AES192/256 the key size is proportionally larger.

#include "nativeui/util/aes.h"

#include <string.h>

// The number of columns comprising a state in AES.
// This is a constant in AES. Value=4.
#define Nb 4

#if defined(AES256) && (AES256 == 1)
  #define Nk 8
  #define Nr 14
#elif defined(AES192) && (AES192 == 1)
  #define Nk 6
  #define Nr 12
#else
  #define Nk 4   // The number of 32 bit words in a key.
  #define Nr 10  // The number of rounds in AES Cipher.
#endif

namespace nu {

namespace {

// State - array holding the intermediate results during decryption.
typedef uint8_t state_t[4][4];

// The lookup-tables are marked const so they can be placed in read-only
// storage instead of RAM.
// The numbers below can be computed dynamically trading ROM for RAM -
// This can be useful in (embedded) bootloader applications, where ROM is often limited.
const uint8_t sbox[256] = {
  //0     1    2      3     4    5     6     7      8    9     A      B    C     D     E     F
  0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
  0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
  0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
  0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
  0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
  0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
  0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
  0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
  0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
  0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
  0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
  0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
  0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
  0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
  0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
  0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16,
};

static const uint8_t rsbox[256] = {
  0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
  0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
  0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
  0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25,
  0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92,
  0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
  0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06,
  0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b,
  0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
  0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e,
  0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b,
  0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
  0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f,
  0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef,
  0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
  0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d,
};

// The round constant word array, Rcon[i], contains the values given by
// x to the power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8)
const uint8_t Rcon[11] = {
  0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36
};

// Jordan Goulder points out in PR #12:
// https://github.com/kokke/tiny-AES-C/pull/12
// that you can remove most of the elements in the Rcon array, because they are
// unused.
//
// From Wikipedia's article on the Rijndael key schedule:
// https://en.wikipedia.org/wiki/Rijndael_key_schedule#Rcon
//
// "Only the first some of these constants are actually used – up to rcon[10]
//  for AES-128 (as 11 round keys are needed), up to rcon[8] for AES-192, up
//  to rcon[7] for AES-256. rcon[0] is not used in AES algorithm."

inline uint8_t getSBoxValue(uint8_t num) {
  return sbox[num];
}

inline uint8_t getSBoxInvert(uint8_t num) {
  return rsbox[num];
}

// This function produces Nb(Nr+1) round keys. The round keys are used in each
// round to decrypt the states.
void KeyExpansion(uint8_t* RoundKey, const uint8_t* Key) {
  uint8_t tempa[4];  // used for the column/row operations

  // The first round key is the key itself.
  for (int i = 0; i < Nk; ++i) {
    RoundKey[(i * 4) + 0] = Key[(i * 4) + 0];
    RoundKey[(i * 4) + 1] = Key[(i * 4) + 1];
    RoundKey[(i * 4) + 2] = Key[(i * 4) + 2];
    RoundKey[(i * 4) + 3] = Key[(i * 4) + 3];
  }

  // All other round keys are found from the previous round keys.
  for (int i = Nk; i < Nb * (Nr + 1); ++i) {
    int k = (i - 1) * 4;
    tempa[0] = RoundKey[k + 0];
    tempa[1] = RoundKey[k + 1];
    tempa[2] = RoundKey[k + 2];
    tempa[3] = RoundKey[k + 3];

    if (i % Nk == 0) {
      // This function shifts the 4 bytes in a word to the left once.
      // [a0,a1,a2,a3] becomes [a1,a2,a3,a0]

      // Function RotWord()
      int k = tempa[0];
      tempa[0] = tempa[1];
      tempa[1] = tempa[2];
      tempa[2] = tempa[3];
      tempa[3] = k;

      // SubWord() is a function that takes a four-byte input word and
      // applies the S-box to each of the four bytes to produce an output word.

      // Function Subword()
      tempa[0] = getSBoxValue(tempa[0]);
      tempa[1] = getSBoxValue(tempa[1]);
      tempa[2] = getSBoxValue(tempa[2]);
      tempa[3] = getSBoxValue(tempa[3]);

      tempa[0] = tempa[0] ^ Rcon[i/Nk];
    }

#if defined(AES256) && (AES256 == 1)
    if (i % Nk == 4) {
      // Function Subword()
      tempa[0] = getSBoxValue(tempa[0]);
      tempa[1] = getSBoxValue(tempa[1]);
      tempa[2] = getSBoxValue(tempa[2]);
      tempa[3] = getSBoxValue(tempa[3]);
    }
#endif

    int j = i * 4;
    k = (i - Nk) * 4;
    RoundKey[j + 0] = RoundKey[k + 0] ^ tempa[0];
    RoundKey[j + 1] = RoundKey[k + 1] ^ tempa[1];
    RoundKey[j + 2] = RoundKey[k + 2] ^ tempa[2];
    RoundKey[j + 3] = RoundKey[k + 3] ^ tempa[3];
  }
}

// This function adds the round key to state.
// The round key is added to the state by an XOR function.
void AddRoundKey(uint8_t round, state_t* state, uint8_t* RoundKey) {
  for (int i = 0; i < 4; ++i)
    for (int j = 0; j < 4; ++j)
      (*state)[i][j] ^= RoundKey[(round * Nb * 4) + (i * Nb) + j];
}

// The SubBytes Function Substitutes the values in the state matrix with values
// in an S-box.
void SubBytes(state_t* state) {
  for (int i = 0; i < 4; ++i)
    for (int j = 0; j < 4; ++j)
      (*state)[j][i] = getSBoxValue((*state)[j][i]);
}

// The ShiftRows() function shifts the rows in the state to the left.
// Each row is shifted with different offset.
// Offset = Row number. So the first row is not shifted.
void ShiftRows(state_t* state) {
  uint8_t temp;

  // Rotate first row 1 columns to left.
  temp           = (*state)[0][1];
  (*state)[0][1] = (*state)[1][1];
  (*state)[1][1] = (*state)[2][1];
  (*state)[2][1] = (*state)[3][1];
  (*state)[3][1] = temp;

  // Rotate second row 2 columns to left.
  temp           = (*state)[0][2];
  (*state)[0][2] = (*state)[2][2];
  (*state)[2][2] = temp;

  temp           = (*state)[1][2];
  (*state)[1][2] = (*state)[3][2];
  (*state)[3][2] = temp;

  // Rotate third row 3 columns to left
  temp           = (*state)[0][3];
  (*state)[0][3] = (*state)[3][3];
  (*state)[3][3] = (*state)[2][3];
  (*state)[2][3] = (*state)[1][3];
  (*state)[1][3] = temp;
}

inline uint8_t xtime(uint8_t x) {
  return ((x<<1) ^ (((x>>7) & 1) * 0x1b));
}

// MixColumns function mixes the columns of the state matrix.
void MixColumns(state_t* state) {
  for (int i = 0; i < 4; ++i) {
    uint8_t Tmp, Tm, t;
    t   = (*state)[i][0];
    Tmp = (*state)[i][0] ^ (*state)[i][1] ^ (*state)[i][2] ^ (*state)[i][3] ;
    Tm  = (*state)[i][0] ^ (*state)[i][1] ; Tm = xtime(Tm);  (*state)[i][0] ^= Tm ^ Tmp ;
    Tm  = (*state)[i][1] ^ (*state)[i][2] ; Tm = xtime(Tm);  (*state)[i][1] ^= Tm ^ Tmp ;
    Tm  = (*state)[i][2] ^ (*state)[i][3] ; Tm = xtime(Tm);  (*state)[i][2] ^= Tm ^ Tmp ;
    Tm  = (*state)[i][3] ^ t ;              Tm = xtime(Tm);  (*state)[i][3] ^= Tm ^ Tmp ;
  }
}

// Multiply is used to multiply numbers in the field GF(2^8).
inline uint8_t Multiply(uint8_t x, uint8_t y) {
  return (((y & 1) * x) ^
         ((y>>1 & 1) * xtime(x)) ^
         ((y>>2 & 1) * xtime(xtime(x))) ^
         ((y>>3 & 1) * xtime(xtime(xtime(x)))) ^
         ((y>>4 & 1) * xtime(xtime(xtime(xtime(x))))));
}

// MixColumns function mixes the columns of the state matrix.
// The method used to multiply may be difficult to understand for the
// inexperienced.
// Please use the references to gain more information.
void InvMixColumns(state_t* state) {
  for (int i = 0; i < 4; ++i) {
    uint8_t a, b, c, d;
    a = (*state)[i][0];
    b = (*state)[i][1];
    c = (*state)[i][2];
    d = (*state)[i][3];

    (*state)[i][0] = Multiply(a, 0x0e) ^ Multiply(b, 0x0b) ^ Multiply(c, 0x0d) ^ Multiply(d, 0x09);
    (*state)[i][1] = Multiply(a, 0x09) ^ Multiply(b, 0x0e) ^ Multiply(c, 0x0b) ^ Multiply(d, 0x0d);
    (*state)[i][2] = Multiply(a, 0x0d) ^ Multiply(b, 0x09) ^ Multiply(c, 0x0e) ^ Multiply(d, 0x0b);
    (*state)[i][3] = Multiply(a, 0x0b) ^ Multiply(b, 0x0d) ^ Multiply(c, 0x09) ^ Multiply(d, 0x0e);
  }
}

// The SubBytes Function Substitutes the values in the state matrix with values
// in an S-box.
void InvSubBytes(state_t* state) {
  for (int i = 0; i < 4; ++i)
    for (int j = 0; j < 4; ++j)
      (*state)[j][i] = getSBoxInvert((*state)[j][i]);
}

void InvShiftRows(state_t* state) {
  uint8_t temp;

  // Rotate first row 1 columns to right.
  temp = (*state)[3][1];
  (*state)[3][1] = (*state)[2][1];
  (*state)[2][1] = (*state)[1][1];
  (*state)[1][1] = (*state)[0][1];
  (*state)[0][1] = temp;

  // Rotate second row 2 columns to right.
  temp = (*state)[0][2];
  (*state)[0][2] = (*state)[2][2];
  (*state)[2][2] = temp;

  temp = (*state)[1][2];
  (*state)[1][2] = (*state)[3][2];
  (*state)[3][2] = temp;

  // Rotate third row 3 columns to right.
  temp = (*state)[0][3];
  (*state)[0][3] = (*state)[1][3];
  (*state)[1][3] = (*state)[2][3];
  (*state)[2][3] = (*state)[3][3];
  (*state)[3][3] = temp;
}

// Cipher is the main function that encrypts the PlainText.
void Cipher(state_t* state, uint8_t* RoundKey) {
  // Add the First round key to the state before starting the rounds.
  AddRoundKey(0, state, RoundKey);

  // There will be Nr rounds.
  // The first Nr-1 rounds are identical.
  // These Nr-1 rounds are executed in the loop below.
  for (uint8_t round = 1; round < Nr; ++round) {
    SubBytes(state);
    ShiftRows(state);
    MixColumns(state);
    AddRoundKey(round, state, RoundKey);
  }

  // The last round is given below.
  // The MixColumns function is not here in the last round.
  SubBytes(state);
  ShiftRows(state);
  AddRoundKey(Nr, state, RoundKey);
}

void InvCipher(state_t* state, uint8_t* RoundKey) {
  // Add the First round key to the state before starting the rounds.
  AddRoundKey(Nr, state, RoundKey);

  // There will be Nr rounds.
  // The first Nr-1 rounds are identical.
  // These Nr-1 rounds are executed in the loop below.
  for (uint8_t round = (Nr - 1); round > 0; --round) {
    InvShiftRows(state);
    InvSubBytes(state);
    AddRoundKey(round, state, RoundKey);
    InvMixColumns(state);
  }

  // The last round is given below.
  // The MixColumns function is not here in the last round.
  InvShiftRows(state);
  InvSubBytes(state);
  AddRoundKey(0, state, RoundKey);
}

void XorWithIv(uint8_t* buf, uint8_t* iv) {
  // The block in AES is always 128bit no matter the key size.
  for (int i = 0; i < AES_BLOCKLEN; ++i)
    buf[i] ^= iv[i];
}

}  // namespace

bool AES::Init(const std::string& key, const std::string& iv) {
  if (key.size() != AES_BLOCKLEN || iv.size() != AES_BLOCKLEN)
    return false;
  KeyExpansion(round_key_, (uint8_t*)(key.data()));
  memcpy(iv_, (uint8_t*)(iv.data()), AES_BLOCKLEN);
  is_valid_ = true;
  return true;
}

void AES::CBCEncryptBuffer(uint8_t* buf, uint32_t len) {
  uint8_t* iv = iv_;
  for (uint32_t i = 0; i < len; i += AES_BLOCKLEN) {
    XorWithIv(buf, iv);
    Cipher((state_t*)buf, round_key_);
    iv = buf;
    buf += AES_BLOCKLEN;
  }
  // store Iv in ctx for next call.
  memcpy(iv_, iv, AES_BLOCKLEN);
}

void AES::CBCDecryptBuffer(uint8_t* buf, uint32_t len) {
  uint8_t storeNextIv[AES_BLOCKLEN];
  for (uint32_t i = 0; i < len; i += AES_BLOCKLEN) {
    memcpy(storeNextIv, buf, AES_BLOCKLEN);
    InvCipher((state_t*)buf, round_key_);
    XorWithIv(buf, iv_);
    memcpy(iv_, storeNextIv, AES_BLOCKLEN);
    buf += AES_BLOCKLEN;
  }
}

}  // namespace nu
